(1) The bicyclic cascade regulation of glutamine synthetase (GS) in E. coli involves 4 protein components, GS, regulatory protein, adenylyltransferase, and uridylyltransferase. Using polyclonal antibodies derived against them, their intracellular concentrations were measured. (2) The bicyclic cascade was reconstituted by mixing the 4 proteins in accordance with the ratio determined in vivo. The state of adenylylation of GS and the state of uridylylation of regulatory protein were measured at various concentrations of glutamine and Alpha-ketoglutarate. Then the sensitivity indexes with respect to glutamine and Alpha-ketoglutarate were obtained. (3) S. cerevisiae contains 2 forms of GS, active and inactive. Several lines of evidence (molecular weight, antibody cross-reactivity, peptide analyses) indicate that they are the same gene products. (4) Kinetic parameters of active and inactive forms of yeast GS were measured. (5) The active form of GS was characterized in detail. Amino acid sequence of several peptides including acetylated N-terminal peptides were established. Sulfhydryl contents, sedimentation coefficients optical properties were also measured. (6) Strong subunit interaction in the octameric yeast GS was revealed. (7) Yeast extracts contain a protein which can provide protection against the oxidative inactivation of several enzymes including GS. This noble protein was purified to homogeneity and its capacity to protect against various oxidative modification systems was measured.